This invention relates to a semiconductor integrated circuit device and also to a method of manufacturing the same. More particularly, the invention relates to a technique which is effective for application to wirings formed by a so-called damascene method wherein, after formation of grooves for wirings in an insulating film, a conductive film is buried inside the grooves.
In recent years, as advances are being made in the scaling-down and multi-layered formation of wirings in a semiconductor integrated circuit device, a so-called damacene technique has been studied, as described, for example, by T. Saito et. al., in Proceedings of International Interconnect Technology Conference, 1998, pp. 160-162 and the like, in which after formation of a groove for wirings in an insulating film, a conductive film is buried inside the groove.
In Japanese laid-open patent Application No. Hei 8 (1996)-222568, a technique is described wherein a groove for wiring is formed in an insulating film and a barrier layer made of a TiN (titanium nitride) thin film is formed according to a CVD (chemical vapor deposition) method, after which a copper thin film is formed on the barrier layer and the copper thin film is etched back, followed by further formation of a protective film made of a TiN thin film and subsequent etching to leave the protective film on the resultant copper thin film wiring.
In the technical report of Mitsubishi Electric Corporation in 1997, pp333-336, a technique is described wherein a barrier layer, such as TiWN or the like, is provided on the upper surface of a copper damascene wiring.
We have recognized the following problem involved in a technique not known in the art when wirings are formed according to the so-called damascene technique wherein, after formation of a groove for wiring in such an insulating film as mentioned above, a conductive film is buried inside the groove to form a wiring.
For instance, copper is usually used as the conductive film. Copper (Cu) has a property such that, when compared with other metals, such as aluminum (Al), tungsten (W) and the like, copper is more liable to be diffused into a silicon oxide film which is being used as the insulating film. When a silicon oxide film is formed directly on the conductive film, the copper at the contact portion is oxidized, thereby permitting the wiring resistance to rise.
Accordingly, a study of the barrier layer which covers the wiring becomes important. Of the barrier films covering such wiring, a titanium nitride (TiN) film has been studied with respect to the barrier film formed inside the groove for the wiring. Likewise, silicon nitride (SiN) has been studied for use as a film (cap film) covering the upper portion of the wiring.
However, in order to prevent the diffusion and oxidation of copper by means of the silicon nitride film covering the wiring on the upper portion thereof, it is necessary that the silicon nitride film be formed to have a certain thickness. Since the silicon nitride film has a high dielectric constant, the RC time constant of the wiring becomes great, thereby impeding the high-speed operation of the device.
Electromigration may occur owing to the diffusion of copper inside the copper wiring or at the copper surface. As a result of our study on the ease of diffusion of copper, it was supposed that when a copper-barrier film interface was compared with a copper-silicon nitride film interface, the activation energy of diffusion at the copper-barrier film interface was greater (i.e. copper was more unlikely to be diffused at the copper-barrier film interface). Accordingly, the electromigration life is determined by the activation energy value of diffusion of copper at the copper-silicon oxide film interface.
Where an upper wiring is further formed on the copper wiring through an insulating film, wherein the copper wiring and the upper wiring are connected with each other through a plug formed in the insulating film, the silicon nitride film over the copper wiring has been removed so as to permit contact, under which the bottom surface of the plug is in direct contact with the copper of the lower wiring. This is liable to cause the concentration of an electric current through the current path from the plug bottom to the lower copper wiring, thereby causing electromigration to occur. Moreover, when voids are formed beneath the plug due to the influence of electromigration, the area of contact between the plug and the lower copper wiring becomes small, thereby leading to the accelerated lowering of the wiring life.
When the plug is formed, a contact hole is also made. In this case or when the contact hole is etched at the bottom thereof so as to improve the contact characteristic, the copper wiring per se at the bottom of the contact hole is also sputter-etched. This allows copper to be deposited on the side walls of the contact hole. As set out hereinabove, such copper is liable to be diffused in the insulating film, thus bringing about a lowering of the breakdown voltage and an increased leakage current.
For burying the conductive film in the groove for wiring, a copper film is, for example, formed on the insulating film, including the inner portion of the groove for wiring, followed by removal of an additional copper film outside the group by chemical mechanical polishing (CMP). At that time, it may be inevitable that recesses or other defects occur. Thereafter, when a silicon nitride film is formed on the copper wiring, voids are formed at the defective portions, with the possibility that electromigration is undesirably caused to start from the void.
Further, where a mask for the contact hole is shifted relative to the lower copper wiring, a fine recess may occur at a side portion of the lower wiring. It is difficult to bury a plug in such a fine recess, thus leading to the formation of a void like that of the above case, with the possibility of creating a starting point for electromigration. In this case, because an area of contact between the plug and the lower wiring is reduced owing to the shifting of the mask, under which condition, when the void is moved toward the interface of the contact, the connection between the plug and the lower wiring is not ensured, resulting in a connection failure.
It is accordingly an object of the invention to provide a semiconductor integrated circuit device and a method of manufacture thereof wherein a cap conductive film is formed on a wiring, thereby realizing high speed operation of the device.
It is another object of the invention to provide a semiconductor integrated circuit device and a method of manufacture thereof wherein an elongated wiring life is ensured, while suppressing electromigration and stress migration from occurring.
It is a further object of the invention to provide a semiconductor integrated circuit device and a method of manufacture thereof wherein the device has an improved dielectric breakdown and has a reduced leakage current achieved by preventing direct sputtering of an underlying copper wiring when a contact hole is etched at the bottom thereof.
It is a still further object of the invention to provide a semiconductor integrated circuit device and a method of manufacture thereof wherein contact failure is reduced even if a contact hole is shifted relative to a wiring.
The above objects and novel features of the invention will become more apparent from the description provided in this specification and from the accompanying drawings.
Typical embodiments of the invention are summarized below.
The method of manufacture of a semiconductor integrated circuit device according to the invention comprises successively forming a barrier layer and a conductive layer within a groove for wiring, removing the barrier layer and the conductive film from outside of the groove for wiring to form the wiring, and forming a cap conductive film on the wiring by selective or preferential growth.
When the cap conductive film is formed on the wiring by selective or preferential growth in this way, the formation of the cap conductive film becomes easy, thus making it possible to realize a high-speed semiconductor integrated circuit device. Moreover, the occurrence of electromigration or stress migration can be suppressed, while providing an elongated wiring life. When a contact hole formed on the wiring is etched at the bottom thereof, direct sputtering of the underlying wiring can be prevented. Thus, dielectric breakdown is reduced, and the reduction of leakage current can be realized. In addition, even when the contact hole is shifted relative to the wiring, the required contact can be maintained and contact failure can be reduced.
The wiring is made, for example, of copper (Cu), silver (Ag), aluminum (Al) or an alloy comprising the above-mentioned metal or metals as a main component. For the cap conductive film, a tungsten (W) film is used, for example. The cap conductive film may be a film of tungsten nitride (WN), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN) or nickel (Ni). The cap conductive film can be formed at a pressure of 1 Torr (1xc3x971.33322xc3x97102 Pa) or below.
An insulating film on the cap conductive film may be formed of a laminated film consisting of a TEOS (tetraethylorthosilicate) film or a carbon-containing silicon insulating film and a film having a dielectric constant lower than the above-mentioned film. Alternatively, the insulating film on the cap conductive film may be formed of a diffusion-preventing insulating film for preventing diffusion of a conductor material for the conductive film and a low dielectric insulating film. For the diffusion-preventing insulating film, there may be used, for example, a silicon nitride film, a PSG film, a silicon carbide film or the like. For the low dielectric insulating film, there is, for example, a TEOS film or an SIOF film.
Prior to the formation of the cap conductive film, the substrate surface may be cleaned with a solution containing hydrogen fluoride or the like for removing foreign matter or contaminated metal. Alternatively, prior to the formation of the cap conductive film, the substrate surface may be treated with hydrogen. After the formation of the cap conductive film, the substrate surface may be cleaned with a solution containing hydrogen fluoride (HF) or hydrogen peroxide (H2O2).
As a result of these treatments, a highly reliable cap conductive film can be formed.
The semiconductor integrated circuit device of the invention comprises a barrier layer formed at side walls and at the bottom of a groove for wiring, a conductive film formed on the barrier layer, and a cap conductive film formed on the conductive film.
The formation of the cap conductive film on the conductive film (wiring) in this way ensures the provision of a high-speed semiconductor integrated circuit device. Moreover, the occurrence of electromigration or stress migration can be suppressed, resulting in an elongation of the life of the wiring. In addition, when a contact hole formed on the wiring is etched at the bottom thereof, the direct sputtering of the underlying wiring can be prevented, thus realizing an improvement including reduction of the dielectric breakdown and reduction of the leakage current. If the contact hole is shifted relative to the wiring, the required contact still can be maintained, and thus, the number of contact failures can be reduced.
It will be noted that the wiring is made, for example, of copper, silver, aluminium or an alloy containing these metals as a main component. The cap conductive film is, for example, a W film. The cap conductive film may be a film of WN, TiN, Ta, TaN or Ni. Alternatively, the cap conductive film may be a film which is formed by selective growth or preferential growth, or may be a film which is formed at a pressure of 1 Torr (1xc3x971.33322xc3x97102 Pa) or below. The thickness of the cap conductive film should be uniform within the same plane of the wiring and can be made uniform irrespective of the wiring width. The variation of the thickness of the cap conductive film may be within a range of 50% or below. Moreover, the thickness of the cap conductive film can be made thinner than the barrier layer at the bottom of the groove for wiring. More particularly, the thickness of the cap conductive film ranges, for example, from 2 to 20 nm.
The insulating film on the cap conductive film may be made of a laminated film including a TEOS film or a carbon-containing silicon insulating film and a film whose dielectric constant is lower than the first-mentioned one. Alternatively, the insulating film on the cap conductive film may be made of a diffusion-preventing insulating film for preventing diffusion of a conductor material for the conductive film, and a low dielectric insulating film. For the diffusion-preventing insulating film, there is used, for example, a silicon nitride film, a PSG film or a silicon carbide film. For the low dielectric insulating film, there is used, for example, a TEOS film or an SiOF film.